A wind turbine transfers the energy of the wind into electrical energy. The wind turbine comprises a nacelle that is connected to a tower and a rotor that is connected to the nacelle. The rotor comprises a hub that is rotatable mounted to the nacelle and at least one rotor blade that is mounted to the hub.
The wind interacts with the rotor blade of the wind turbine in a way that the rotor rotates. The rotation of the rotor is transferred to an electrical generator.
When the wind turbine is erected, the tower is set up and the nacelle is mounted onto the tower. The hub is mounted to the nacelle and the at least one rotor blade is mounted to the hub.
The at least one rotor blade is hoisted up by a crane and connected to the hub. The hub has to be in a predetermined angular rotational position around its axis of rotation to establish the connection between the hub and the rotor blade.
This position corresponds to the direction of the blade during the fastening of the connection. The position can be a horizontal or a vertical arrangement of the hub and the rotor blade for example.
The hub has to be rotated to establish the connection between the hub and a first rotor blade. In the case of more then one rotor blade that has to be mounted, the position of the hub has to be changed between the mounting of one rotor blade and the next. The hub has to be rotated from the first into a second position to establish the connection between the hub and the second of the two rotor blades.
US 2006/0147308 A1 describes a method of mounting rotor blades to a rotor hub which is connected to a pod of a wind turbine power installation. The rotor hub is rotated into a predetermined first position. A rotor blade is fitted. The rotor hub is rotated by means of the rotor blade into a predetermined second position. A second rotor blade is mounted. The rotation of the rotor hub is effected in the direction of the effect of gravitational force of the first rotor blade which is already mounted.
This shows the disadvantage that the gravitational force of a first rotor blade will support the rotation into a second position only for a part of the rotation. In a certain second part of the rotation the rotation needs to be performed against the gravitational forces of the first rotor blade. Thus the described method is not reliable enough to perform the rotation of the hub during the installation of the rotor blades.
It is known to rotate the rotor of the wind turbine during the installation of the rotor blades by means of drives.
The installation of the first rotor blade results in an uneven distribution of the weight at the rotor. After the installation of the first rotor blade the rotor needs to the rotated into a second position for the installation of the next rotor blade. This leads to a changing and partially strong load during the rotation. The drive used to rotate the rotor has to be strong enough to overcome the changing and high load. Thus the drive has to be quite large to be able to rotate the rotor.
This leads to the disadvantage that a quite large drive needs to be installed at the wind turbine to rotate the rotor. In addition, the coupling of the drive and the rotor needs to be strong enough to transfer the loads.
U.S. Pat. No. 7,165,941 B2 describes a process for mounting rotor blades to a rotor hub of a wind power installation in situ. The process includes mounting a weight to at least one flange of the rotor hub. A rotor blade is mounted to at least one of the flanges, the hub is rotated into a predetermined position and the weight is exchanged for a rotor blade.
Thus high torque in the mechanical train of the wind power installation in the operation of mounting the rotor blades is avoided.
This shows the disadvantage that the weight is fixed at the position of the blade and needs to be detached when the blade is mounted.